Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored, for example because they can use a wider variety of inks.
Piezoelectric ink jet print heads include an array of piezoelectric elements (i.e., piezoelectric transducers or PZTs). One process to form the array can include detachably bonding a blanket piezoelectric layer to a transfer carrier with an adhesive, and dicing the blanket piezoelectric layer to form a plurality of individual piezoelectric elements. A plurality of dicing saw passes can be used to remove all the piezoelectric material between adjacent piezoelectric elements to provide the correct spacing between each piezoelectric element.
Piezoelectric ink jet print heads can typically further include a flexible diaphragm to which the array of piezoelectric elements is attached. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a power source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
The formation of ink jet printheads typically requires lamination of multiple layers of materials as part of their fabrication. Traditional printhead designs may use layers of gold-plated stainless steel sheet metal with features that are photochemically etched and then brazed together to form robust structures. However, with the continued drive to improve cost and performance, use of alternate materials and bonding processes may be used. While polymer layers can be used as a replacement of some sheet metal components, polymers require adhesives with suitable properties to bond to each other and to metal layers.
For example, the adhesive must be chemically compatible with the inks used within the printhead. Further, the adhesive should have certain physical properties that reduce printhead failures during use. An adhesive should have a good bond strength, a low squeeze out to prevent blocking of the fluid path, and should be sufficiently resistant to oxidation with elevated temperatures during use. Also, some adhesives may increase in weight and swell, or become less compliant and more stiff during use when exposed to certain inks and elevated temperatures, which can result in leakage of ink or other failure modes. Some of these failures may occur only after extended use of the printhead.
Additionally, incompatibility with aqueous inks may swell the adhesive, thereby causing changes in dimensional geometry that will affect jetting performance. For the requirements of printhead modularity design, an adhesive with a lower bonding temperature is needed. Some current adhesives have a bonding temperature of 290° C. or higher, which is above the critical temperatures for some components in the jet stack, for example the PZTs. Therefore a new adhesive is desired to accommodate bonding of all components in an ink jet printhead configured for use with an aqueous ink.